Between 1974 and 1982 it was represented by Bruce Douglas-Mann who was elected as a Labour MP but defected in 1982 to the Social Democratic Party (SDP). Douglas-Mann was the sole SDP defector to resign his seat; he sought immediate re-election.

The 2015 re-election of McDonagh made the seat the 41st safest of Labour's 232 seats by percentage of majority and 14th safest in the capital.[3] The seat is one of the capital's two seats in which its majority in 2015 surpassed the Labour Party's landslide 1997 victory (the other being Ilford South).

1983-2010: Upon redrawing of most of the local government wards, the London Borough of Merton wards of Colliers Wood, Figge's Marsh, Graveney, Lavender, Longthornton, Lower Morden, Phipps Bridge, Pollards Hill, Ravensbury, and St Helier.

The seat is relatively dense suburban — predominantly the housing divides into terraced houses and low-rise apartments in southern parts of Tooting and Streatham at the northern end of the seat. In the south-west of the constituency is the most affluent part, Lower Morden. The name Mitcham and Morden is a partial misnomer — the area of the modern town centre around Morden tube station is in the Wimbledon constituency.

In the middle, the former coaching stop town of Mitcham with its ancient cricket green retains some village-like characteristics and had relatively poor transport connections during the seat's tenure until the building of the Croydon Tramlink. In the 20th century, Mitcham became surrounded by modern council housing and light industry. Housing varies between the large rented sector, privately acquired properties much of which due to the Thatcher Ministry-introduced right to buy and significant dependence in certain areas on social housing.[4]

Across the borough, around 40% of the population are ethnic minorities.[5][6]